The exit() function causes normal program termination and the the value
of status & 0377 is returned to the parent (see wait(2)).
All functions registered with atexit() and on_exit() are called
in the reverse order of their registration, and all open streams are flushed
and closed. Files created by tmpfile() are removed.
The C standard specifies two defines EXIT_SUCCESS and EXIT_FAILURE
that may be passed to exit() to indicate successful or unsuccessful
During the exit processing, it is possible to register additional functions with
atexit() and on_exit(). Always the last-registered function is
removed from the chain of registered functions, and invoked. It is undefined
what happens if during this processing either exit() or
longjmp() is called.
The use of EXIT_SUCCESS and EXIT_FAILURE is slightly more portable (to non-Unix
environments) than that of 0 and some nonzero value like 1 or -1. In
particular, VMS uses a different convention.
BSD has attempted to standardize exit codes - see the file
After exit(), the exit status must be transmitted to the parent process.
There are three cases. If the parent has set SA_NOCLDWAIT, or has set the
SIGCHLD handler to SIG_IGN, the status is discarded. If the parent was waiting
on the child it is notified of the exit status. In both cases the exiting
process dies immediately. If the parent has not indicated that it is not
interested in the exit status, but is not waiting, the exiting process turns
into a "zombie" process (which is nothing but a container for the
single byte representing the exit status) so that the parent can learn the
exit status when it later calls one of the wait() functions.
If the implementation supports the SIGCHLD signal, this signal is sent to the
parent. If the parent has set SA_NOCLDWAIT, it is undefined whether a SIGCHLD
signal is sent.
If the process is a session leader and its controlling terminal the controlling
terminal of the session, then each process in the foreground process group of
this controlling terminal is sent a SIGHUP signal, and the terminal is
disassociated from this session, allowing it to be acquired by a new
If the exit of the process causes a process group to become orphaned, and if any
member of the newly-orphaned process group is stopped, then a SIGHUP signal
followed by a SIGCONT signal will be sent to each process in this process